1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a semiconductor device in which an etching of silicon oxide film can be stopped at a predetermined position.
2. Description of the Related Art
Such a semiconductor device is known in which a plurality of insulating films having different etching rates are successively deposited. The structure is employed either for an automated stop in an etching to make a trench or a hole or for making a self-aligned via-hole between interconnection patterns or between an interconnection pattern and an active region.
FIG. 1 is a schematic cross-sectional view of a conventional semiconductor device described in the Proceedings of International Symposium on VMIC (VLSI Multilevel Interconnection Conference), P. 15 (June, 1993). In the semiconductor device, an interconnection layer 17 is formed within a trench formed in laminated insulating films including polyimide films 15 and silicon nitride films 16 deposited on a substrate 1. The silicon nitride film 16 functions here as an etch-stop layer for blocking an etching executed for patterning the polyimide film 15.
In addition to the combination of polyimide and silicon nitride films as described above, other combinations of insulating films which allow a selective etching include a combination of a silicon dioxide film which contains phosphorus atoms or boron atoms and a substantially pure silicon dioxide film which does not substantially contain impurities (described in the Journal of Vacuum Science and Technology A, Vol. 11, P. 279 (1993)), a combination of a silicon dioxide film and an aluminum oxide film (described in the Technical Digest of IEDM (International Electron Devices Meeting), P. 837 (1992) and a combination of a silicon dioxide film and a silicon nitride film (described in the Technical Digest of IEDM, P. 473 (1990)).
When two or more kinds of insulating films having different etching rates are used in a semiconductor device for the purposes described above, the difference in etching rates should be sufficiently large to obtain a high selectivity and each of the combined films should not adversely affect the device characteristics. The aforesaid combinations, however, have problems as described below.
In a case of a combination of a silicon dioxide film which contains phosphorus or boron atoms and a substantially pure silicon dioxide film, gases containing moistures are released during etching for forming contact-holes (via-holes used for a first-level interconnection, being referred to as "via-holes" hereinafter) or via-holes, thereby rendering the electric characteristics of semiconductor devices unstable because of a highly hygroscopic property in an oxide film containing phosphorus or boron atoms. When those films are used as an interlayer insulating film, moisture contained therein causes a corrosion in a metallic interconnection, deteriorating a reliability of semiconductor devices. Similarly, in the case of a combination of a polyimide film and a silicon nitride film, all of released gases, a high hygroscopic property and a thermal instability of the polyimide film adversely affect the device characteristics of semiconductor devices.
Further, in a case of a combination of a silicon nitride and a silicon dioxide films, a difference in electric characteristics between two films such as permittivity induces a band discontinuity at the interface therebetween while an intermittent deposition is likely to induce an interfacial energy level. Those band discontinuity and interfacial levels are apt to trap the electric charges at the interface during a plasma processing. The trapped charges have an adverse effect on the semiconductor device characteristics, for example, shifts or fluctuations in threshold voltage of FETs in the semiconductor devices.
Furthermore, in a case of a combination of a silicon dioxide film and an aluminum oxide film, problems similar to those of the combination of a silicon nitride film and a silicon dioxide film will arise because the film properties are greatly different from each other. The fluctuations in the device characteristics described above cause a deviation from designed specifications as well as cause malfunctions in the operation of the electric circuits formed in the semiconductor device.